The invention relates to an apparatus for quantitatively definite delivery of a fluid or thick, pressurized medium such as paint, varnish, glue or the like.
Great numbers of such devices are commercially available, for example, hand-held spray guns having a built-in electrical swinging armature drive and an attached paint reservoir. All of these known devices are activated by activating the pump drive, whereupon the pump begins to operate and the liquid or thick medium is conveyed under pressure to the delivery nozzle. The pump drive is then switched off in order to end the work process. A significant disadvantage in such a system is that the pressure, especially the spraying pressure required for a faultless delivery of the medium, is not present when work is begun, but is only built up after a few strokes of the pump mechanism, the result being that the nebulization or atomization is unsatisfactory at the beginning of the spraying phase, for example, when spraying paint. The same thing occurs when the work process is ended, i.e., a so-called "after-drip" occurs. Further, all of the known devices share the disadvantage that the throughput quantity of the medium to be delivered can be varied per time unit only within a comparatively small range because of adjustment of the pump stroke is only possible to a limited extent.
It is therefore an object of the present invention to improve spray guns of the type initially cited, such that delivery of the medium occurs only when the required delivery pressure is reached and such that the throughput quantity can be varied over a relatively broad range in a simple way.
These and other objects of this invention will become apparent from the following disclosure and appended claims.